Method for controlling a modulation index of a near field communication device with aid of dynamic calibration, and associated apparatus

ABSTRACT

A method for controlling a modulation index of a near field communication (NFC) device includes: in a calibration mode of the NFC device, temporarily coupling a receiver of the NFC device to a transmitter of the NFC device to form a probing path between the receiver and the transmitter; and in the calibration mode of the NFC device, dynamically adjusting at least one portion of a plurality of modulation parameters corresponding to the modulation index according to probed results of outputs of the transmitter, in order to calibrate the modulation index, for use of transmitting through the transmitter in a normal mode of the NFC device. An associated apparatus is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/816,953, which was filed on Apr. 29, 2013, and is included herein byreference.

BACKGROUND

The present invention relates to dynamic modulation index calibrationfor near field communication (NFC) devices, and more particularly, to amethod for controlling a modulation index of an NFC device, and to anassociated apparatus.

According to the related art, a conventional NFC device can be designedto communicate using a predetermined ASK data rate. In practice, it istypically needed to make sure of a proper value of the modulation indexin advance (e.g., in a design phase of the conventional NFC device, orduring manufacturing the conventional NFC device), in order to achievebetter performance of the conventional NFC device. As the modulationindex depends on many factors such as the antenna size of theconventional NFC device, the proximity of the target antenna (e.g. thedistance between the antenna of the conventional NFC device and thetarget antenna of another device), and the NFC antenna matching networkof the conventional NFC device, some problems may occur. For example,the designer of the conventional NFC device may have designed theconventional NFC device based upon a wrong assumption of the proximityof the target antenna, causing the performance of the conventional NFCdevice to become unacceptable to the user in some situations. In anotherexample, the manufacturer of the conventional NFC device may need tomanually adjust the conventional NFC device for different target valueof the modulation index, causing the associated costs such as additionallabor costs of manually adjusting the conventional NFC device to beirreducible. In another example, as the modulation index depends on theantenna impedance, and as the antenna impedance is typically sensitiveto the environment that shifts its resonance frequency due to magneticfield coupling, in a situation where a metallic surface, a secondaryantenna in close proximity, etc. change the antenna impedancedrastically, the performance of the conventional NFC device may becomeunacceptable to the user. Thus, a novel method is required for improvingthe modulation index control of the NFC device in various kinds ofsituations.

SUMMARY

It is an objective of the claimed invention to provide a method forcontrolling a modulation index of a near field communication (NFC)device, and to provide an associated apparatus, in order to solve theabove-mentioned problems.

It is another objective of the claimed invention to provide a method forcontrolling a modulation index of an NFC device, and to an associatedapparatus, in order to enhance the performance by performing dynamicmodulation index calibration.

According to at least one preferred embodiment, a method for controllinga modulation index of an NFC device is provided, where the methodcomprises: in a calibration mode of the NFC device, temporarily couplinga receiver of the NFC device to a transmitter of the NFC device to forma probing path between the receiver and the transmitter; and in thecalibration mode of the NFC device, dynamically adjusting at least oneportion of a plurality of modulation parameters corresponding to themodulation index according to probed results of outputs of thetransmitter, in order to calibrate the modulation index, for use oftransmitting through the transmitter in a normal mode of the NFC device.

According to at least one preferred embodiment, an apparatus forcontrolling a modulation index of an NFC device is provided, where theapparatus comprises at least one portion of the NFC device. Theapparatus comprises a transmitter, a receiver, and a control circuit,where the transmitter, the receiver, and the control circuit arepositioned within a chip of the NFC device, and the control circuit iscoupled to the transmitter and the receiver. The transmitter is arrangedto transmit data for the NFC device, and the receiver is arranged toreceive data for the NFC device. In addition, in a calibration mode ofthe NFC device, the receiver is temporarily coupled to the transmitterto form a probing path between the receiver and the transmitter.Additionally, the control circuit is arranged to control operations ofthe NFC device, wherein in the calibration mode of the NFC device, thecontrol circuit dynamically adjusts at least one portion of a pluralityof modulation parameters corresponding to the modulation index accordingto probed results of outputs of the transmitter, in order to calibratethe modulation index, for use of transmitting through the transmitter ina normal mode of the NFC device.

It is an advantage of the present invention that the present inventionmethod and apparatus can dynamically tune the modulation index at anytime, for example, the modulation index calibration can be triggered anytime either upon power on or by software sequence. In addition, incomparison to the related art, the present invention method andapparatus can reduce the related costs since changing the design of theNFC device in response to the change of the antenna size or shape is notrequired. Additionally, as the modulation index tuning of the presentinvention method and apparatus can be performed adaptively, theperformance for each data rate can be optimized.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an apparatus for controlling a modulation indexof a near field communication (NFC) device according to a firstembodiment of the present invention.

FIG. 2 illustrates an NFC system comprising the aforementioned NFCdevice of the embodiment shown in FIG. 1 according to an embodiment ofthe present invention.

FIG. 3 illustrates a flowchart of a method for controlling a modulationindex of an NFC device according to an embodiment of the presentinvention.

FIG. 4 illustrates a control scheme involved with the method shown inFIG. 3 according to an embodiment of the present invention.

FIG. 5 illustrates some associated signals involved with the methodshown in FIG. 3 according to an embodiment of the present invention.

FIG. 6 illustrates a working flow involved with the method shown in FIG.3 according to an embodiment of the present invention.

DETAILED DESCRIPTION

Certain terms are used throughout the following description and claims,which refer to particular components. As one skilled in the art willappreciate, electronic equipment manufacturers may refer to a componentby different names. This document does not intend to distinguish betweencomponents that differ in name but not in function. In the followingdescription and in the claims, the terms “include” and “comprise” areused in an open-ended fashion, and thus should be interpreted to mean“include, but not limited to . . . ”. Also, the term “couple” isintended to mean either an indirect or direct electrical connection.Accordingly, if one device is coupled to another device, that connectionmay be through a direct electrical connection, or through an indirectelectrical connection via other devices and connections.

Please refer to FIG. 1, which illustrates a diagram of an apparatus 100for controlling a modulation index of a near field communication (NFC)device according to a first embodiment of the present invention, wherethe apparatus 100 may comprise at least one portion (e.g. a portion orall) of the NFC device. For example, the apparatus 100 may comprise aportion of the NFC device mentioned above, and more particularly, can beat least one hardware circuit such as at least one integrated circuit(IC) within the NFC device. In another example, the apparatus 100 can bethe whole of the NFC device mentioned above. In another example, theapparatus 100 may comprise an NFC system comprising the NFC devicementioned above.

As shown in FIG. 1, the apparatus 100 may comprise a chip 110, which canbe taken as an example of the aforementioned at least one IC, and mayfurther comprise an antenna matching network and electromagneticinterference (EMI) filtering module 130 (labeled “Antenna matchingnetwork and EMI filtering” in FIG. 1, for brevity) and an NFC antenna140, where the antenna matching network and EMI filtering module 130 maycomprise an antenna matching network and an EMI filter (which are notillustrated, for brevity). In practice, the EMI filter mentioned abovecan be implemented with some impedance components (e.g. one or moreinductors and/or one or more capacitors, in this embodiment), and theantenna matching network mentioned above can be implemented with someimpedance components (e.g. one or more inductors and/or one or morecapacitors, in this embodiment). In addition, the chip 110 may comprisea control circuit such as a digital baseband circuit 112, and maycomprise a serving module 114 (labeled “Sx” in FIG. 1, for brevity). Thecontrol circuit such as a digital baseband circuit 112 is arranged tocontrol operations of the NFC device. Additionally, the chip 110 mayfurther comprise a transceiver and rectifier module 118 (labeled “Tx/Rx& Rectifier” in FIG. 1, for brevity). For example, the transceiver andrectifier module 118 may comprise a transmitter 118T (labeled “Tx” inFIG. 1, for brevity), a receiver 118R (labeled “Rx” in FIG. 1, forbrevity), and a rectifier 118C. When needed, the serving module 114 iscapable of providing the transmitter 118T and the receiver 118R with asignal LO2 having a frequency (e.g. 13.56 MHz) and a signal LO1 havinganother frequency (e.g. 12.05 MHz), respectively. As shown in FIG. 1,the transmitter 118T can be coupled to a set of transmitter terminalsTXP and TXN of the chip 110, where the transmitter 118T is arranged totransmit data for the NFC device through the set of transmitterterminals TXP and TXN, the antenna matching network and EMI filteringmodule 130, and the NFC antenna 140. The receiver 118R can be coupled toa set of receiver terminals RXP and RXN of the chip 110, where thereceiver 118R is arranged to receive data for the NFC device through theset of receiver terminals RXP and RXN, the antenna matching network andEMI filtering module 130, and the NFC antenna 140. The rectifier 118Ccan be coupled to a set of card terminals CardP and CardN of the chip110, where the rectifier 118C is arranged to perform rectifying, energyharvesting and passive load modulation operations for the NFC devicethrough the set of card terminals CardP and CardN.

As shown in FIG. 1, the signals LO1 and LO2 are illustrated for bettercomprehension. This is for illustrative purposes only, and is not meantto be a limitation of the present invention. According to somevariations of this embodiment, the architecture of the apparatus 100 isnot limited to utilize a specific type of receivers such asdirect-conversion receivers. For example, another type of receivers suchas direct sampling receivers can be utilized in the architecture of theapparatus 100 in some of these variations, and other types of receiverscan be utilized in the architecture of the apparatus 100 in others ofthese variations.

FIG. 2 illustrates an NFC system 200 comprising the aforementioned NFCdevice of the embodiment shown in FIG. 1 according to an embodiment ofthe present invention, where the polling device 210 and the listeningdevice 220 may represent two NFC terminals of the NFC system 200. Asshown in FIG. 2, the polling device 210 and the listening device 220 mayhave their own electronic circuits, respectively, and may have their ownNFC antennas.

For better comprehension, the listening device 220 can be taken as anexample of the NFC device mentioned above, and the polling device 210can be taken as an example of the other device in the embodiment shownin FIG. 1. According to this embodiment, the NFC system 200 may transmitdata in different data rates between the aforementioned two NFCterminals such as the polling device 210 and the listening device 220.For example, the polling device 210 can be an NFC reader and thelistening device 220 can be a passive tag or card. As the listeningdevice 220 may need to operate in the absence of battery power, thelistening device 220 can be designed to harvest energy from the incomingfield (labeled “FIELD” in FIG. 2) such as at least one portion of theelectromagnetic field.

With aid of using the architecture shown in FIG. 1, in a situation wherethe modulation index can be dynamically adjusted, and more particularly,can be calibrated to be suitable for the environment of the NFC system200, the related art problems can be resolved.

FIG. 3 illustrates a flowchart of a method 300 for controlling amodulation index of an NFC device according to an embodiment of thepresent invention. The method 300 shown in FIG. 3 can be applied to theapparatus 100 shown in FIG. 1, and more particularly, can be applied tothe chip 110 shown in FIG. 1. The method is described as follows.

In Step 310, in a calibration mode of the NFC device, the receiver 118Ris temporarily coupled to the transmitter 118T to form a probing pathbetween the receiver 118R and the transmitter 118T. For example, aswitching unit may be installed on the probing path, for selectivelyactivating or deactivating the probing path, and the digital basebandcircuit 112 may temporarily couple the receiver 118R to the transmitter118T by turning on the switching unit to activate the probing path. Thisis for illustrative purposes only, and is not meant to be a limitationof the present invention. In another example, it is unnecessary toinstall the switching unit mentioned above, where the receiver 118R iscoupled to the transmitter 118T to form the probing path between thereceiver 118R and the transmitter 118T.

In Step 320, in the calibration mode of the NFC device, the digitalbaseband circuit 112 dynamically adjusts at least one portion of aplurality of modulation parameters corresponding to the modulation indexaccording to the probed results of the outputs of the transmitter 118T,in order to calibrate the modulation index, for use of transmittingthrough the transmitter 118T in a normal mode of the NFC device.Typically, the digital baseband circuit 112 turns on both of thereceiver 118R and the transmitter 118T, and some calibration operationsmay be performed in the calibration mode.

More particularly, the serving module 114, which is positioned withinthe chip 110 of the NFC device and coupled to the digital basebandcircuit 112 and both of the transmitter 118T and the receiver 118R, isarranged to provide the transmitter 118T with a first signal having afirst frequency (e.g. the signal LO2 having the frequency of 13.56 MHz)in the calibration mode of the NFC device, and to provide the receiver118R with a second signal having a second frequency (e.g. the signal LO1having the frequency of 12.05 MHz) in the calibration mode of the NFCdevice, allowing the receiver 118R to extract intermediate frequency(IF) signals from the probed results, for use of calibrating themodulation index, where the first frequency is a frequency of a carrierfor data transmission through the transmitter 118T in the normal mode ofthe NFC device, and the second frequency is different from the firstfrequency.

FIG. 4 illustrates a control scheme involved with the method 300 shownin FIG. 3 according to an embodiment of the present invention. As shownin FIG. 4, the serving module 114 of this embodiment may comprise anoscillator (labeled “OSC” in FIG. 4, for brevity) and a set of frequencydividers (labeled “DIV1” and “DIV2” in FIG. 4, for brevity). The set offrequency dividers can be utilized for performing frequency dividingoperations on the output of the oscillator to generate the first signalmentioned above (e.g. the signal LO2 having the frequency of 13.56 MHz)and the second signal mentioned above (e.g. the signal LO1 having thefrequency of 12.05 MHz). In this embodiment, the receiver 118R iscoupled to the transmitter 118T through at least one impedance componentto form the probing path between the receiver 118R and the transmitter118T. For example, the aforementioned at least one impedance componentmay comprise the resistor and the capacitor illustrated around the upperright of FIG. 4. More particularly, one of the set of receiver terminalsRXP and RXN, such as the receiver terminal RXP shown in FIG. 4, istemporarily coupled to one of the set of transmitter terminals TXP andTXN of the transmitter 118T (e.g. the transmitter terminal TXP shown inFIG. 4) through the antenna matching network and EMI filtering module130 to form the probing path between the receiver 118R and thetransmitter 118T, where the probed results can be received by thereceiver 118R through the aforementioned one of the set of receiverterminals RXP and RXN, such as the receiver terminal RXP shown in FIG.4.

According to this embodiment, the receiver 118R may comprise a firstconversion unit and a second conversion unit, where the first conversionunit is arranged to, in the calibration mode of the NFC device, convertthe probed results received through the aforementioned one of the set ofreceiver terminals RXP and RXN according to the second signal togenerate a first portion of the intermediate signals, and the secondconversion unit is arranged to, in the calibration mode of the NFCdevice, convert the probed results received through the aforementionedone of the set of receiver terminals RXP and RXN according to a phaseshifted signal of the second signal to generate a second portion of theintermediate signals. More particularly, the first conversion unit andthe second conversion unit can be a first mixer and a second mixer(which are illustrated around the upper right and the lower right of thereceiver 118R shown in FIG. 4, respectively), and the receiver 118R maycomprise a 90-degree phase shifting unit (labeled “90°” in FIG. 4, forbrevity), and may further comprise a set of filters respectively coupledto the output terminals of the first mixer and the second mixer, a setof programmable-gain amplifiers (PGAs) respectively coupled to theoutput terminals of the set of filters, and a set of analog-to-digitalconverters (ADCs) respectively coupled to the output terminals of theset of PGAs. For example, in the calibration mode of the NFC device, thefirst mixer is arranged to mix the probed results received through theaforementioned one of the set of receiver terminals RXP and RXN, such asthe receiver terminal RXP shown in FIG. 4, with the second signal (e.g.the signal LO1 having the frequency of 12.05 MHz) to generate theaforementioned first portion of the intermediate signals. In addition,in the calibration mode of the NFC device, the second mixer is arrangedto mix the probed results received through the aforementioned one of theset of receiver terminals RXP and RXN, such as the receiver terminal RXPshown in FIG. 4, with the phase shifted signal of the second signalmentioned above (e.g. the phase shifted signal of the signal LO1 havingthe frequency of 12.05 MHz) to generate the aforementioned secondportion of the intermediate signals, where the phase shifted signal inthis embodiment can be a 90-degree phase shifted signal generated fromthe 90-degree phase shifting unit. In practice, the set of filters canbe utilized for filtering the intermediate signals mentioned above,where the filtered results of the intermediate signals are input intothe set of PGAs. The set of PGAs can be utilized for amplifying thefiltered results of the intermediate signals according to a gain controlparameter DA_PGA_GC[5:0] of the set of PGAs of the receiver 118R, withthe gain of any of the set of PGAs corresponding to the controlparameter DA_PGA_GC[5:0]. The set of ADCs can be utilized for performinganalog-to-digital conversion operations on the amplified results outputfrom the set of PGAs (i.e. the amplified results of the filtered resultsof the intermediate signals) to generate digital outputs AD_ADC_ID[5:0]and AD_ADC_QD[5:0] corresponding to the I-channel and the Q-channel,respectively.

Please note that, in the embodiment shown in FIG. 4, some details of thereceiver 118R are illustrated for better comprehension. This is forillustrative purposes only, and is not meant to be a limitation of thepresent invention. According to some variations of this embodiment, thearchitecture of the apparatus 100 is not limited to utilize a specifictype of receivers such as direct-conversion receivers. For example,another type of receivers such as direct sampling receivers can beutilized in the architecture of the apparatus 100 in some of thesevariations, and other types of receivers can be utilized in thearchitecture of the apparatus 100 in others of these variations.

As shown in FIG. 4, the transmitter 118T may comprise a multiplexer(labeled “MUX” in FIG. 4, for brevity), and may further comprise a poweramplifier (labeled “PA” in FIG. 4, for brevity). The multiplexer isarranged to multiplex the aforementioned modulation parameters such asthe modulation parameters RG_PA_A_OUT[7:0] and DA_PA_B_OUT[7:0]according to a modulation data signal MOD_DATA in any of the calibrationmode and the normal mode, where the modulation data signal MOD_DATA isutilized for carrying data in the normal mode. Based on the first signalmentioned above (e.g. the signal LO2 having the frequency of 13.56 MHz),the power amplifier is arranged to generate the outputs of thetransmitter 118T (i.e. the outputs mentioned in Step 320, such as a setof differential outputs in this embodiment) according to the multiplexedresult output from the multiplexer. For example, in a situation wherethe multiplexed result is the modulation parameter RG_PA_A_OUT[7:0], theamplitude of the outputs of the transmitter 118T corresponds to themodulation parameter RG_PA_A_OUT[7:0], where the frequency of theoutputs of the transmitter 118T is equivalent to that of the firstsignal mentioned above (e.g. 13.56 MHz). In another example, in asituation where the multiplexed result is the modulation parameterDA_PA_B_OUT[7:0], the amplitude of the outputs of the transmitter 118Tcorresponds to the modulation parameter DA_PA_B_OUT[7:0], where thefrequency of the outputs of the transmitter 118T is equivalent to thatof the first signal mentioned above (e.g. 13.56 MHz).

FIG. 5 illustrates some associated signals involved with the method 300shown in FIG. 3 according to an embodiment of the present invention.Please note that the output signals obtained from the output terminalsof the set of PGAs mentioned above can be regarded as a set ofdifferential outputs, and the PGA output signal PGA_OUT shown in FIG. 5may represents the voltage difference between the output terminals ofthe set of PGAs.

In this embodiment, the modulation data signal MOD_DATA may correspondto a logical value 0 or a logical value 1, where the lower level of thetwo voltage levels of the modulation data signal MOD_DATA shown in FIG.5 indicates the logical value 0, and the higher level of the two voltagelevels of the modulation data signal MOD_DATA shown in FIG. 5 indicatesthe logical value 1. For example, in a situation where the modulationdata signal MOD_DATA corresponds to the logical value 1, the multiplexedresult is the modulation parameter RG_PA_A_OUT[7:0], and the amplitudeVmax of the outputs of the transmitter 118T corresponds to themodulation parameter RG_PA_A_OUT[7:0]. More particularly, in thecalibration mode, with the amplitude Vmax of the outputs of thetransmitter 118T corresponding to the modulation parameterRG_PA_A_OUT[7:0], the amplitude Vmax′ of the PGA output signal PGA_OUToutput from the set of PGAs mentioned above can be detected, where theratio of the amplitude Vmax′ of the PGA output signal PGA_OUT to theamplitude Vmax of the outputs of the transmitter 118T can be adjusted bytuning the control parameter DA_PGA_GC[5:0] mentioned above. In anotherexample, in a situation where the modulation data signal MOD_DATAcorresponds to the logical value 0, the multiplexed result is themodulation parameter DA_PA_B_OUT[7:0], and the amplitude Vmin of theoutputs of the transmitter 118T corresponds to the modulation parameterDA_PA_B_OUT[7:0]. More particularly, in the calibration mode, with theamplitude Vmin of the outputs of the transmitter 118T corresponding tothe modulation parameter DA_PA_B_OUT[7:0], the amplitude Vmin′ of thePGA output signal PGA_OUT output from the set of PGAs mentioned abovecan be detected, where the ratio of the amplitude Vmin′ of the PGAoutput signal PGA_OUT to the amplitude Vmin of the outputs of thetransmitter 118T can be adjusted by tuning the control parameterDA_PGA_GC[5:0] mentioned above. This is for illustrative purposes only,and is not meant to be a limitation of the present invention. Accordingto some variations of this embodiment, the architecture may be varied,where the PGA gain can be adjusted so that the signal falls within theADC dynamic range. In practice, in the calibration mode, the digitalbaseband circuit 112 is capable of tuning the control parameterDA_PGA_GC[5:0] to calibrate the ratio of the amplitude Vmax′ to theamplitude Vmax or the ratio of the amplitude Vmin′ to the amplitudeVmin, in order to calibrate the aforementioned modulation index, whichcan be expressed as follows:

m=(Vmax−Vmin)/(Vmax+Vmin);

where the notation “m” may represent the modulation index.

According to this embodiment, in the calibration mode of the NFC device,the digital baseband circuit 112 may temporarily sets the modulationdata signal MOD_DATA to correspond to the logical value 1, and sets afirst modulation parameter of the modulation parameters RG_PA_A_OUT[7:0]and DA_PA_B_OUT[7:0] to be equivalent to a specific value, in order tocalibrate the gain control parameter DA_PGA_GC[5:0] of the set of PGAsof the receiver 118R. This is for illustrative purposes only, and is notmeant to be a limitation of the present invention. According to somevariations of this embodiment, the architecture may be varied, where thePGA gain can be adjusted so that the signal falls within the ADC dynamicrange. More particularly, the first modulation parameter is utilized forcontrolling the maximum voltage of the envelope of the outputs of thetransmitter 118T (e.g. the amplitude Vmax) in any of the calibrationmode and the normal mode, where the modulation parameterRG_PA_A_OUT[7:0] can be taken as an example of the first modulationparameter mentioned above.

In addition, in the calibration mode of the NFC device, after thecalibration of the gain control parameter DA_PGA_GC[5:0] is completed,the digital baseband circuit 112 may calculate an average of somedetection values of the maximum voltage mentioned above (e.g. theaverage of some detection values of the amplitude Vmax, such as theamplitude Vmax′), where the detection values are obtained based on aportion of a plurality of digitized values of the PGA outputs of the setof PGAs. For example, in a situation where the digital outputsAD_ADC_ID[5:0] and AD_ADC_QD[5:0] carry the plurality of digitizedvalues mentioned above, the digital baseband circuit 112 may averagesome of the digitized values carried by the digital outputsAD_ADC_ID[5:0] and AD_ADC_QD[5:0] to obtain the average mentioned above.The digital baseband circuit 112 may further calculate a targetdetection value of the minimum voltage of the envelope of the outputs ofthe transmitter 118T (e.g. the target detection value of the amplitudeVmin, such as the target value of the amplitude Vmin′) according to theaverage and according to a target value of the modulation index m. Forexample, the target value of the modulation index m can be equivalent to10% based on NFC standards. In another example, the target value of themodulation index m can be equivalent to 30% based on NFC standards. Thisis for illustrative purposes only, and is not meant to be a limitationof the present invention. In another example, the target value of themodulation index m can be equivalent to another value. No matter whetherthe target value of the modulation index m is equivalent to 10% or 30%or another value, after the target detection value of the minimumvoltage mentioned above (e.g. the target detection value of theamplitude Vmin, such as the target value of the amplitude Vmin′) iscalculated, the digital baseband circuit 112 may temporarily set themodulation data signal MOD_DATA to correspond to the logical value 0, inorder to calibrate a second modulation parameter of the modulationparameters RG_PA_A_OUT[7:0] and DA_PA_B_OUT[7:0] according to the targetdetection value of the minimum voltage. More particularly, the secondmodulation parameter is utilized for controlling the minimum voltage ofthe envelope of the outputs of the transmitter 118T (e.g. the amplitudeVmin) in any of the calibration mode and the normal mode, where themodulation parameter DA_PA_B_OUT[7:0] can be taken as an example of thesecond modulation parameter mentioned above.

Additionally, the digital baseband circuit 112 may dynamically adjustthe second modulation parameter (e.g. the modulation parameterDA_PA_B_OUT[7:0]), in order to complete calibrating the modulation indexm. For example, the digital baseband circuit 112 may dynamically adjustthe second modulation parameter (e.g. the modulation parameterDA_PA_B_OUT[7:0]) until one detection value of the minimum voltage isequivalent to the target detection value mentioned above, where theaforementioned one detection value is obtained based on another portionof the plurality of digitized values of the PGA outputs of the set ofPGAs. This is for illustrative purposes only, and is not meant to be alimitation of the present invention. According to some variations ofthis embodiment, the digital baseband circuit 112 may dynamically adjustthe second modulation parameter (e.g. the modulation parameterDA_PA_B_OUT[7:0]) until the aforementioned one detection value of theminimum voltage is substantially closest to the target detection value.More particularly, the digital baseband circuit 112 may dynamicallyadjust the second modulation parameter (e.g. the modulation parameterDA_PA_B_OUT[7:0]) until the difference between the aforementioned onedetection value falls within the range of a predetermined intervalcomprising the target detection value. For example, the notationmag_vmin_tgt may represent the target detection value, and thepredetermined interval can be [mag_vmin_tgt−Δ, mag_vmin_tgt+Δ], wherethe notation Δ may represent the predetermined tolerance of the targetdetection value mag_vmin_tgt. According to some other variations of thisembodiment, the aforementioned one detection value of the minimumvoltage may be extended to be at least one detection value (e.g. one ormore detection values) of the minimum voltage to guarantee thecorrectness of the calibration in some situations, where theaforementioned at least one detection value is obtained based on theother portion of the plurality of digitized values of the PGA outputs ofthe set of PGAs. According to some other variations of this embodiment,the digital baseband circuit 112 may dynamically adjust the secondmodulation parameter (e.g. the modulation parameter DA_PA_B_OUT[7:0])until the aforementioned at least one detection value (e.g. theaforementioned one or more detection values) is substantially closest tothe target detection value. More particularly, the digital basebandcircuit 112 may dynamically adjust the second modulation parameter (e.g.the modulation parameter DA_PA_B_OUT[7:0]) until the difference betweenthe aforementioned at least one detection value falls within the rangeof the predetermined interval comprising the target detection value.

In practice, in the calibration mode of the NFC device, after the gaincontrol parameter DA_PGA_GC[5:0] is calibrated, the gain controlparameter DA_PGA_GC[5:0] is not varied. In addition, the probed resultsof the outputs of the transmitter 118T are typically obtained throughthe probing path mentioned above.

In some embodiments of the present invention, such as some variations ofthis embodiment, the probing path is not activated in the normal mode ofthe NFC device. This is for illustrative purposes only, and is not meantto be a limitation of the present invention.

FIG. 6 illustrates a working flow 600 involved with the method 300 shownin FIG. 3 according to an embodiment of the present invention.

In Step 610, the digital baseband circuit 112 checks whether any radiofrequency (RF) field exists around the NFC device (labeled “RF fielddetected” in FIG. 6, for better comprehension). More particularly, undercontrol of the digital baseband circuit 112, the NFC device detects ifthere is a field or not, where the airways must be clear of any fieldbefore calibration starts, and if there is no field, then calibrationoperations can be performed. When it is detected that the RF fieldexists, Step 610 is re-entered; otherwise, Step 620 is entered.

In Step 620, the digital baseband circuit 112 sets the modulation datasignal MOD_DATA to correspond to the logical value 1 (labeled“MOD_DATA=1” in FIG. 6, for brevity).

In Step 630, the digital baseband circuit 112 calibrates the gaincontrol parameter DA_PGA_GC[5:0] (labeled “PGA Gain” in FIG. 6, forbrevity). As a result, the digital baseband circuit 112 controls thegain control parameter DA_PGA_GC[5:0] to be a certain value to guaranteethat the amplitude Vmin′ mentioned above can be properly detected. Thisis for illustrative purposes only, and is not meant to be a limitationof the present invention. According to some variations of thisembodiment, the architecture may be varied, where the receiver gain (orthe Rx gain, such as the PGA gain mentioned above) can be adjusted sothat the received signal falls within the ADC dynamic range. For thebest overall calibration performance in this embodiment, the digitalbaseband circuit 112 does not further vary the gain control parameterDA_PGA_GC[5:0] in the following steps of the working flow 600.

In Step 640, the digital baseband circuit 112 obtains gets the averagemagnitude avg_mag, which can be taken as an example of the averagementioned in the embodiment shown in FIG. 5. More particularly, thedigital baseband circuit 112 obtains at least one portion of theplurality of digitized values of the PGA outputs of the set of PGAs fromthe digital outputs AD_ADC_ID[5:0] and AD_ADC_QD[5:0], and calculatesthe average magnitude avg_mag of the magnitude (or amplitude) of thewaveform of the PGA output signal PGA_OUT.

In Step 650, the digital baseband circuit 112 sets the parametermag_vmax to be equal to the average magnitude avg_mag (labeled“mag_vmax=avg_mag” in FIG. 6, for brevity), where the parameter mag_vmaxrepresents the aforementioned amplitude Vmax′ of the PGA output signalPGA_OUT output from the set of PGAs mentioned above.

In Step 660, the digital baseband circuit 112 computes the targetdetection value mag_vmin_tgt (e.g. the target detection value of theamplitude Vmin, such as the target value of the amplitude Vmin′). Forexample, the target detection value mag_vmin_tgt can be calculatedaccording to the following equation:

mag _(—) vmin_tgt=((1−m_tgt)/(1+m_tgt))*mag _(—) vmax;

where the notation m_tgt represents the target value of the modulationindex m. For example, the target value m_tgt of the modulation index mcan be equivalent to 10% based on NFC standards. In another example, thetarget value m_tgt of the modulation index m can be equivalent to 30%based on NFC standards. In another example, the target value m_tgt ofthe modulation index m can be equivalent to another value.

In Step 670, the digital baseband circuit 112 sets the modulation datasignal MOD_DATA to correspond to the logical value 0 (labeled“MOD_DATA=0” in FIG. 6, for brevity).

In Step 680, the digital baseband circuit 112 calibrates the amplitudeVmin mentioned above by dynamically adjusting the second modulationparameter (e.g. the modulation parameter DA_PA_B_OUT[7:0]) and by usingthe target detection value mag_vmin_tgt as the target of the amplitudeVmin′. For example, the digital baseband circuit 112 may dynamicallyadjust the second modulation parameter (e.g. the modulation parameterDA_PA_B_OUT[7:0]) until the amplitude Vmin′ reaches the target detectionvalue mag_vmin_tgt. In another example, the digital baseband circuit 112may dynamically adjust the second modulation parameter (e.g. themodulation parameter DA_PA_B_OUT[7:0]) until the amplitude Vmin′approaches the target detection value mag_vmin_tgt and falls with therange of the predetermined interval [mag_vmin_tgt−Δ, mag_vmin_tgt+Δ],where the notation Δ may represent the predetermined tolerance of thetarget detection value mag_vmin_tgt. As a result of completing thecalibration of the amplitude Vmin, the modulation index m is properlycalibrated, where the measurement results of the modulation index mshould be equal to or very close to the target value m_tgt, and someexperiments using real silicon chips indicate that the overallperformance of the NFC device can be guaranteed.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method for controlling a modulation index of anear field communication (NFC) device, the method comprising: in acalibration mode of the NFC device, temporarily coupling a receiver ofthe NFC device to a transmitter of the NFC device to form a probing pathbetween the receiver and the transmitter; and in the calibration mode ofthe NFC device, dynamically adjusting at least one portion of aplurality of modulation parameters corresponding to the modulation indexaccording to probed results of outputs of the transmitter, in order tocalibrate the modulation index, for use of transmitting through thetransmitter in a normal mode of the NFC device.
 2. The method of claim1, further comprising: in the calibration mode of the NFC device,providing the transmitter with a first signal having a first frequency,wherein the first frequency is a frequency of a carrier for datatransmission through the transmitter in the normal mode of the NFCdevice; and in the calibration mode of the NFC device, providing thereceiver with a second signal having a second frequency, allowing thereceiver to extract intermediate signals from the probed results, foruse of calibrating the modulation index, wherein the second frequency isdifferent from the first frequency.
 3. The method of claim 2, whereinthe receiver is coupled to a set of receiver terminals of the chip, andthe transmitter is coupled to a set of transmitter terminals of thechip; and the step of temporarily coupling the receiver of the NFCdevice to the transmitter of the NFC device to form the probing pathbetween the receiver and the transmitter further comprises: temporarilycoupling one of the set of receiver terminals to one of the set oftransmitter terminals of the transmitter to form the probing pathbetween the receiver and the transmitter; wherein the probed results arereceived through the one of the set of receiver terminals.
 4. The methodof claim 3, further comprising: in the calibration mode of the NFCdevice, converting the probed results received through the one of theset of receiver terminals according to the second signal to generate afirst portion of the intermediate signals; and in the calibration modeof the NFC device, converting the probed results received through theone of the set of receiver terminals according to a phase shifted signalof the second signal to generate a second portion of the intermediatesignals.
 5. The method of claim 1, wherein a multiplexer within thetransmitter is utilized for multiplexing the modulation parametersaccording to a modulation data signal in any of the calibration mode andthe normal mode; the modulation data signal is utilized for carryingdata in the normal mode; and the step of dynamically adjusting the atleast one portion of the plurality of modulation parameterscorresponding to the modulation index according to the probed results ofthe outputs of the transmitter in order to calibrate the modulationindex further comprises: in the calibration mode of the NFC device,temporarily setting the modulation data signal to correspond to alogical value 1, and setting a first modulation parameter of themodulation parameters to be equivalent to a specific value, in order tocalibrate a gain control parameter of a set of programmable-gainamplifiers (PGAs) of the receiver, wherein the first modulationparameter is utilized for controlling a maximum voltage of an envelopeof the outputs of the transmitter in any of the calibration mode and thenormal mode; wherein a first portion of the intermediate signals and asecond portion of the intermediate signals are input into the set ofPGAs, respectively.
 6. The method of claim 5, wherein the step ofdynamically adjusting the at least one portion of the plurality ofmodulation parameters corresponding to the modulation index according tothe probed results of the outputs of the transmitter in order tocalibrate the modulation index further comprises: in the calibrationmode of the NFC device, after calibration of the gain control parameteris completed, calculating an average of detection values of the maximumvoltage, wherein the detection values are obtained based on a portion ofa plurality of digitized values of PGA outputs of the set of PGAs;calculating a target detection value of a minimum voltage of theenvelope of the outputs of the transmitter according to the average andaccording to a target value of the modulation index; and temporarilysetting the modulation data signal to correspond to a logical value 0,in order to calibrate a second modulation parameter of the modulationparameters according to the target detection value of the minimumvoltage, wherein the second modulation parameter is utilized forcontrolling the minimum voltage of the envelope of the outputs of thetransmitter in any of the calibration mode and the normal mode.
 7. Themethod of claim 6, wherein the step of calibrating the second modulationparameter of the modulation parameters according to the target detectionvalue of the minimum voltage further comprises: dynamically adjustingthe second modulation parameter until at least one detection value ofthe minimum voltage is substantially closest to the target detectionvalue, wherein the at least one detection value is obtained based onanother portion of the plurality of digitized values of the PGA outputsof the set of PGAs.
 8. The method of claim 5, wherein in the calibrationmode of the NFC device, after the gain control parameter is calibrated,the gain control parameter is not varied.
 9. The method of claim 1,wherein the probing path is not activated in the normal mode of the NFCdevice.
 10. The method of claim 1, wherein the probed results of theoutputs of the transmitter are obtained through the probing path.
 11. Anapparatus for controlling a modulation index of a near fieldcommunication (NFC) device, the apparatus comprising at least oneportion of the NFC device, the apparatus comprising: a transmitter,positioned within a chip of the NFC device, arranged to transmit datafor the NFC device; a receiver, positioned within the chip of the NFCdevice, arranged to receive data for the NFC device, wherein in acalibration mode of the NFC device, the receiver is temporarily coupledto the transmitter to form a probing path between the receiver and thetransmitter; and a control circuit, positioned within the chip of theNFC device and coupled to the transmitter and the receiver, arranged tocontrol operations of the NFC device, wherein in the calibration mode ofthe NFC device, the control circuit dynamically adjusts at least oneportion of a plurality of modulation parameters corresponding to themodulation index according to probed results of outputs of thetransmitter, in order to calibrate the modulation index, for use oftransmitting through the transmitter in a normal mode of the NFC device.12. The apparatus of claim 11, further comprising: a serving module,positioned within the chip of the NFC device and coupled to the controlcircuit and both of the transmitter and the receiver, arranged toprovide the transmitter with a first signal having a first frequency inthe calibration mode of the NFC device, and to provide the receiver witha second signal having a second frequency in the calibration mode of theNFC device, allowing the receiver to extract intermediate signals fromthe probed results, for use of calibrating the modulation index, whereinthe first frequency is a frequency of a carrier for data transmissionthrough the transmitter in the normal mode of the NFC device, and thesecond frequency is different from the first frequency.
 13. Theapparatus of claim 12, wherein the receiver is coupled to a set ofreceiver terminals of the chip, and the transmitter is coupled to a setof transmitter terminals of the chip; one of the set of receiverterminals is temporarily coupled to one of the set of transmitterterminals of the transmitter to form the probing path between thereceiver and the transmitter; and the probed results are receivedthrough the one of the set of receiver terminals.
 14. The apparatus ofclaim 13, wherein the receiver comprises: a first conversion unitarranged to, in the calibration mode of the NFC device, convert theprobed results received through the one of the set of receiver terminalsaccording to the second signal to generate a first portion of theintermediate signals; and a second conversion unit arranged to, in thecalibration mode of the NFC device, convert the probed results receivedthrough the one of the set of receiver terminals according to a phaseshifted signal of the second signal to generate a second portion of theintermediate signals.
 15. The apparatus of claim 11, wherein thetransmitter comprises: a multiplexer arranged to multiplex themodulation parameters according to a modulation data signal in any ofthe calibration mode and the normal mode, wherein the modulation datasignal is utilized for carrying data in the normal mode; wherein in thecalibration mode of the NFC device, the control circuit temporarily setsthe modulation data signal to correspond to a logical value 1, and setsa first modulation parameter of the modulation parameters to beequivalent to a specific value, in order to calibrate a gain controlparameter of a set of programmable-gain amplifiers (PGAs) of thereceiver, wherein the first modulation parameter is utilized forcontrolling a maximum voltage of an envelope of the outputs of thetransmitter in any of the calibration mode and the normal mode.
 16. Theapparatus of claim 15, wherein in the calibration mode of the NFCdevice, after calibration of the gain control parameter is completed,the control circuit calculates an average of detection values of themaximum voltage, wherein the detection values are obtained based on aportion of a plurality of digitized values of PGA outputs of the set ofPGAs; the control circuit calculates a target detection value of aminimum voltage of the envelope of the outputs of the transmitteraccording to the average and according to a target value of themodulation index; and the control circuit temporarily sets themodulation data signal to correspond to a logical value 0, in order tocalibrate a second modulation parameter of the modulation parametersaccording to the target detection value of the minimum voltage, whereinthe second modulation parameter is utilized for controlling the minimumvoltage of the envelope of the outputs of the transmitter in any of thecalibration mode and the normal mode.
 17. The apparatus of claim 16,wherein the control circuit dynamically adjusts the second modulationparameter until at least one detection value of the minimum voltage issubstantially closest to the target detection value, wherein the atleast one detection value is obtained based on another portion of theplurality of digitized values of the PGA outputs of the set of PGAs. 18.The apparatus of claim 15, wherein in the calibration mode of the NFCdevice, after the gain control parameter is calibrated, the gain controlparameter is not varied.
 19. The apparatus of claim 11, wherein theprobing path is not activated in the normal mode of the NFC device. 20.The apparatus of claim 11, wherein the probed results of the outputs ofthe transmitter are obtained through the probing path.